Many types of medical apparatus are implanted at various locations in the body on a permanent or semi-permanent basis. However, after implantation it is often difficult to obtain information from the implanted apparatus. One such type of implantable apparatus is a shunt valve and catheter used in the treatment of hydrocephalus, a condition where cerebrospinal fluid (CSF) collects in the ventricles of the brain of a patient. CSF is produced by the ventricular system and is normally absorbed by the venous system. However, if the CSF is not absorbed, the volume of CSF increases thereby elevating the intracranial pressure. This excess CSF can result in abnormally high epidural and intradural pressures. Left untreated, hydrocephalus can result in serious medical conditions, including subdural hematoma, compression of the brain tissue and impaired blood flow.
Various drainage catheters or shunt systems have been developed to remove excess CSF and thereby reduce the elevated intracranial pressure. Generally, fluid shunt systems include a valve mechanism for controlling or regulating the flow rate of fluid through the system. Shunt systems typically permit fluid flow only when the fluid pressure reaches a threshold pressure for the shunt valve. The threshold pressure should be such that excessive fluid is allowed to drain without creating an undesirable overdrainage condition in which too much fluid is drained from the ventricle. Thus, the shunt system should have a threshold pressure that is balanced to reduce excessive intracranial pressure and avoid overdrainage conditions.
To achieve optimal drainage conditions, it may be desirable to periodically adjust the threshold pressure. For example, a surgeon may initially select a relatively low threshold pressure to trigger fluid flow. Over time, the initial threshold pressure may not be ideal. For example, it could lead to excess fluid flow, creating an undesirable overdrainage condition in which too much fluid is drained from the ventricle. Such a situation may give rise to a need to increase the threshold pressure to afford a fluid flow rate that is balanced to avoid both excessive intracranial pressure and overdrainage conditions.
One prior art shunt valve that allows threshold pressure adjustment without removal of the device is disclosed in U.S. Pat. Nos. 4,615,691 and 4,772,257, both of which are incorporated by reference herein. These patents disclose a cerebrospinal fluid shunt valve that is externally adjustable by means of a programming device. The shunt valve includes a stepping motor having rotor and stator elements. The stator elements are composed of a magnetically soft and permeable material shaped and positioned with respect to the rotor. The external programming device applies a magnetic field causing the rotor to rotate about a central axis so as to adjust the threshold pressure.
After programming the shunt valve and during examinations, the pressure setting of the device should be verified to ensure proper fluid drainage occurs. The pressure setting is generally ascertained using X-ray examination of the device. Known shunt valves and stepping motors generally include radiopaque elements that are observable on a display or other device. From the observed positions of the radiopaque elements, the pressure to which the device has been programmed can be verified. However, X-ray examination can be cumbersome and time consuming. Furthermore, access to X-ray equipment may be limited or the equipment may be unavailable.
It would, therefore, be desirable to provide a system including an apparatus and a device for obtaining information from the implanted apparatus without invasive surgical procedures and/or X-ray examination.